This invention relates to apparatus for detecting contamination of liquid, and, more particularly, apparatus for detecting contamination of liquid suitable for detecting the quantity of a component insoluble to a solvent such as benzene and contained in engine oil utilized in a diesel engine for operating a bulldozer, for instance.
In a prior art apparatus for measuring the degree of contamination of oil comprises a light emitting member 1, a light receiving member 2 and transparent members 3 for defining therebetween a space 4 having a definite width l as shown in FIG. 1, and a sample of oil is passed through the gap to measure the quantity of the light transmitting through the space 4 thereby determining the degree of contamination of the oil. When the degree of contamination of the oil exceeds 2.5 w/% which is specified as the quantity of the component insoluble to benzene, it is necessary to exchange the oil. The thickness of the oil sample, that is, the width l of the space 4, is generally maintained at about 1 mm.
However, as the engine oil of a diesel engine utilized to drive a bulldozer or the like contains a large quantity of carbon it is impossible to accurately measure the degree of contamination with a measuring width l of about 1 mm. Although the degree of contamination can be measured by decreasing the width l to about 0.01 mm, it is impossible to maintain the measuring width at this value since the temperature of the engine oil varies from 0.degree. to 120.degree. C, especially at the pistons from 0.degree. to 340.degree. C.
Moreover, the reliability and accuracy of the prior art apparatus are impaired by variations in the quantity of the light emanated from the lights source owing to difference in characteristics of the light source and aging of the luminous element. For example, the variation in the quantity of light emanated by a luminous diode amounts to .+-. 20 % per year due to aging. Accordingly, there is a defect that it is impossible to accurately measure the degree of contamination of liquid due to the variations in the characteristics of the light source.